Gliomas are brain tumors originating from glial cells in the nervous system. Glial cells, commonly called neuroglia or simply glia, are non-neuronal cells that provide support and nutrition, maintain homeostasis, form myelin, and participate in signal transmission in the nervous system. The two most important subgroups of gliomas are astrocytomas and oligodendrogliomas, named according to the normal glial cell type from which they originate (astrocytes or oligodendrocytes, respectively). Belonging to the subgroup of astrocytomas, glioblastoma multiforme (referred to as glioblastoma hereinafter) is the most common malignant brain tumor in adults and accounts for approx. 40% of all malignant brain tumors and approx. 50% of gliomas (CBTRUS, 2006). It aggressively invades the central nervous system and is ranked at the highest malignancy level (grade IV) among all gliomas. Although there has been steady progress in their treatment due to improvements in neuroimaging, microsurgery, diverse treatment options such as temozolomide, and radiation, glioblastomas remain incurable (Macdonald, 2001; Burton and Prados, 2000; Prados and Levin, 2000). The lethal rate of this brain tumor is very high: the average life expectancy is 9 to 12 months after first diagnosis. The 5-year survival rate from 1986 to 1990 was 8.0%. To date, the five-year survival rate following aggressive therapy including gross tumor resection is still less than 10% (Burton and Prados, 2000; Nieder et al., 2000; Napolitano et al., 1999; Dazzi et al., 2000). Accordingly, there is a strong medical need for an alternative and effective therapeutic method.
Tumor cells of glioblastomas are the most undifferentiated ones among brain tumors, so the tumor cells have high potential of migration and proliferation and are highly invasive, leading to very poor prognosis. Glioblastomas lead to death due to rapid, aggressive, and infiltrative growth in the brain. The infiltrative growth pattern is responsible for the unresectable nature of these tumors. Glioblastomas are also relatively resistant to radiation and chemotherapy, and, therefore, post-treatment recurrence rates are high. In addition, the immune response to the neoplastic cells is rather ineffective in completely eradicating all neoplastic cells following resection and radiation therapy (Roth and Weller, 1999; Dix et al., 1999; Sablotzki et al., 2000).
Glioblastoma is classified into primary glioblastoma (de novo) and secondary glioblastoma, depending on differences in the gene mechanism during malignant transformation of undifferentiated astrocytes or glial precursor cells. Secondary glioblastoma occurs in a younger population of up to 45 years of age. During 4 to 5 years on average, secondary glioblastoma develops from lower-grade astrocytoma through undifferentiated astrocytoma. In contrast, primary glioblastoma predominantly occurs in an older population with a mean age of 55 years. Generally, primary glioblastoma occurs as fulminant glioblastoma characterized by tumor progression within 3 months from the state with no clinical or pathological abnormalities (Pathology and Genetics of the Nervous Systems. 29-39 (IARC Press, Lyon, France, 2000)).
Glioblastoma migrates along myelinated nerves and spreads widely in the central nervous system. In most cases surgical treatment shows only limited sustainable therapeutic effect (Neurol. Med. Chir. (Tokyo) 34, 91-94, 1994; Neurol. Med. Chir. (Tokyo) 33, 425-458, 1993; Neuropathology 17, 186-188, 1997) (Macdonald, 2001; Prados and Levin, 2000).
Malignant glioma cells evade detection by the host's immune system by producing immunosuppressive agents that impair T cell proliferation and production of the immune-stimulating cytokine IL-2 (Dix et al., 1999).
Intracranial neoplasms can arise from any of the structures or cell types present in the CNS, including the brain, meninges, pituitary gland, skull, and even residual embryonic tissue. The overall annual incidence of primary brain tumors in the United States is 14 cases per 100,000. The most common primary brain tumors are meningiomas, representing 27% of all primary brain tumors, and glioblastomas, representing 23% of all primary brain tumors (whereas glioblastomas account for 40% of malignant brain tumor in adults). Many of these tumors are aggressive and of high grade. Primary brain tumors are the most common solid tumors in children and the second most frequent cause of cancer death after leukemia in children.
The search for effective treatment of glioblastomas in patients is still ongoing today. Immunotherapy, or treatment via recruitment of the immune system, to fight these neoplastic cells has been investigated. First encouraging results were obtained in immuno-therapeutic studies in humans, in which antigen-specific CTL responses could be induced leading to prolonged median survival times compared to that obtained applying standard treatment accompanied by minimal toxicity (Heimberger et al., 2006).
There thus remains a need for a new efficacious and safe treatment option for brain tumors and to enhance the well-being of the patients without using chemotherapeutic agents or other agents that may lead to severe side effects. The present invention fulfils this need.